BRUSSELS (Reuters) -A number of government agencies in the European Union and elsewhere have voiced concerns about security risks as Apple opens up its iPhones and iPads to rival app stores to comply with EU tech rules, Apple said on Friday. Under the Digital Markets Act (DMA), from March 7 Apple will be required to offer alternative app stores on iPhones and allow developers to opt out of using its in-app payment system, which charges fees of up to 30%. The U.S. tech giant, which on Jan. 24 detailed the changesto bring its App Store in line with the EU rules, said "sideloading" - installation of applications on a mobile device without using its dedicated app store - has sparked concerns from both EU and non-EU government agencies and users...